The purpose of the proposed research is to examine the role of specific visual pathways in the recovery of vestibulo-ocular and vestibular neuronal responsiveness following unilateral labyrinth lesions. We will test hypotheses concerning the influence of different inputs to the brainstem and cerebellum that may provide visual signals that promote the development of and are necessary for the maintenance of vestibular compensation. Neurons in the vestibular nuclear complex and prepositus nucleus will be assessed for their responses to linear and angular head acceleration, for visual sensitivity and for oculomotor-related activity, in trained primates, prior to and during recovery from unilateral labyrinthectomy. Those data will be compared with that obtained from additional animals in which hemilabyrinthecomy is preceded by lesions of one of two structures involved in the transmission of signals relayed from visual motion processing areas in the cortex. We hypothesize that lesions of the nucleus of the optic tract, which are known to impair optokinetic responses, will also result in deficits in the recovery of vestibulo-ocular responses to horizontal head acceleration. We will evaluate, in additional animals, another pathway that has been implicated in the early component of optokinetic and smooth pursuit eye movements, the dorsal lateral pontine nucleus, which provides visual inputs to a portion of the vestibulo- cerebellum. Vestibulo-ocular, optokinetic and vestibular neuronal responses will be assessed. The findings of the proposed studies combined with our previous results on the response characteristic of neurons in each visual pathway will provide insights as to the type of visual stimuli that are implicated in the development and maintenance of vestibular compensation. This would in turn suggest strategies for new therapies that could be used in the rehabilitation of patients following labyrinthine injury.